A life of a rolling bearing varies due to a variety of complexly intertwined factors such as a material, a form, a size, a lubricant state, and a load of a bearing ring or a rolling element of the rolling bearing. Accordingly, in order to obtain the rolling bearing which has an appropriate durability according to use, it is necessary to perform a testing in order to know effects which the various factors exert on the life of the rolling bearing. FIG. 6 illustrates a radial rolling-bearing testing device in an example of the related art (for example, refer to Patent Document 1). In the radial rolling-bearing testing, a leading end section (the left end section in FIG. 6) and a portion near to a base end of a rotary shaft 2 are rotatably supported inside a fixed housing 1 by a pair of radial rolling bearings 3 and 3 which each are bearings to be tested. A movable housing 4 is disposed concentrically to the rotary shaft 2 in a periphery of a center section of the rotary shaft 2 which is positioned between the radial rolling bearings 3 and 3. The movable housing 4 is provided inside the fixed housing 1 in a state in which a displacement in the radial direction is possible, and a displacement in a rotation direction is prevented. Then, a support hearing 5 is provided between an inner peripheral surface of the movable housing 4 and an outer peripheral surface at the center section of the rotary shaft 2. Then, lower half sections of the support bearing 5 and the radial rolling bearings 3 and 3 are immersed in lubricant which is retained in a lubricant reservoir 6 that is provided inside the fixed housing 1. According to the need, foreign matters 7 and 7 such as metal powders and ceramic powders are mixed into the lubricant. A radial load F with a desired value which faces a vertical direction (up-and-down direction in FIG. 6) is freely applied to the movable housing 4 by a pressurizing device such as a hydraulic cylinder.
In a case where a life testing of the radial rolling bearings 3 and 3 is performed, the radial rolling bearings 3 and 3 are pressed in the vertical direction via the movable housing 4, the support bearing 5, and the rotary shaft 2 by pressing the movable housing 4 using the pressurizing device, and the rotary shaft 2 is driven so as to rotate. As a result, the life testing for durability evaluation of the radial rolling bearings 3 and 3 can be performed in a state in which the desired radial load F is applied and rotated at the desired rotation speed.
In a case where the radial rolling-bearing testing device with the related art structure described above, there is a possibility that there is a problem as follows. That is, in a case where the movable housing 4 is pressed downward in a vertical direction, the inner ring of the radial rolling bearing 3 is pressed downward in the vertical direction via the rotary shaft 2. As a result, as shown in FIG. 7A, a lower end section (a portion illustrated by a thick line) of the radial rolling bearing 3 is the load zone. That is, a radial load F is applied to the lower end section. Since the lower half section of the radial rolling bearing 3 is immersed in the lubricant, the lubricant state of the load zone is excessive (excessively enhanced), and a testing time increases. Meanwhile, in an upper end section of the support bearing 5 becomes the load zone, and the lubricant in the load zone tends to be insufficient or depleted. As a result, a life of the support bearing 5 shortens, and it is necessary to frequently replace the support bearing 5. There is a possibility that the life of the support bearing 5 becomes shorter than the life of the radial rolling bearing 3, and the life testing of the radial rolling bearing 3 is not able to be normally performed. In contrast to this, in a case where the movable housing 4 is pressed upward in the vertical direction, the inner ring of the radial rolling bearing 3 is pressed upward in the vertical direction via the rotary shaft 2. As a result, as shown in FIG. 7B, the upper end section (a portion illustrated by a thick line) of the radial rolling bearing 3 is the load zone. That is, the radial load F is applied to the upper end section. For this reason, the lubricant tends to be insufficient or depleted in the upper end section which becomes the load zone. Accordingly, in a case where the life testing is performed, there is a possibility that the testing results vary greatly due to whether or not splashes of the lubricant splatter on the upper end section of the radial rolling bearing 3 for some reason. Such variation is remarkable in a case where the foreign matter is mixed into the lubricant.